Re: Questionable code in handling of wordend in the regexp engine in regex-emacs.c

[Alan Mackenzie <acm@muc.de>]

Hello again, Eli.

On Fri, Mar 01, 2019 at 16:38:25 +0000, Alan Mackenzie wrote:
> On Fri, Mar 01, 2019 at 18:22:39 +0200, Eli Zaretskii wrote:
> > > Date: Fri, 1 Mar 2019 14:58:56 +0000
> > > Cc: monnier@iro.umontreal.ca, emacs-devel@gnu.org
> > > From: Alan Mackenzie <acm@muc.de>

[ .... ]

> > Actually, what I had in mind was a simple

> >   eassert (CHAR_HEAD_P (BUF_FETCH_BYTE (b, bytepos)));

> > right at the beginning of buf_bytepos_to_charpos.

[ .... ]

I'm experimenting with:


diff --git a/src/marker.c b/src/marker.c
index b58051a8c2..89b6ca57f4 100644
--- a/src/marker.c
+++ b/src/marker.c
@@ -322,6 +322,9 @@ buf_bytepos_to_charpos (struct buffer *b, ptrdiff_t bytepos)
   ptrdiff_t distance = BYTECHAR_DISTANCE_INITIAL;
 
   eassert (BUF_BEG_BYTE (b) <= bytepos && bytepos <= BUF_Z_BYTE (b));
+  /* Check bytepos is not in the middle of a character. */
+  eassert (bytepos >= BUF_Z_BYTE (b)
+           || CHAR_HEAD_P (BUF_FETCH_BYTE (b, bytepos)));
 
   best_above = BUF_Z (b);
   best_above_byte = BUF_Z_BYTE (b);


After configuring with --enable-checking and building, I tried make
check.  The tests errored out with this bytepos check three times.  In:

    src/coding-tests.log
    lisp/epg-tests.log
    lisp/emacs-lisp/package-tests.log

.  Quite possibly there is just one bug here, but there might be two or
three.  I think it would be best to track it/them down before committing
the change to marker.c.

-- 
Alan Mackenzie (Nuremberg, Germany).